Continuous attempts are made to improve the efficiency of gas turbine engines, and particularly the compressor and/or turbine sections thereof. Compressors and turbines of gas turbine engines comprise rotating turbo-machinery having a plurality of rotor blades, including for example axial compressors, centrifugal compressors (i.e. impellers) and turbines. A major source of inefficiency of such compressors and/or turbines is caused by tip leakage flow, whereby air escapes through the radial tip clearance gap formed between the tips of the rotor blades and the surrounding casing or shroud. As such, attempts to increase compressor/turbine efficiency in general, and to reduce tip leakage flow in particular, continue to be sought.